1. Field of the Invention
The present invention relates to a method for extrusion of compound products starting from a billet which contains a core of one material and a casing of another material.
This is done by applying a sealing ring with greater thickness than the gap between the core and the casing around the rear end of the core, then inserting the core into the casing, and pressing the sealing ring to stick in the gap between the core and the casing so that the sealing ring and/or the casing are deformed. The rear end of the casing is beveled inwardly.
2. The Prior Art
In the production of a tubular product, the core is tubular so that a mandrel forming the hole in the tube can pass through the billet. Extrusion of compound products is described in more detail in, for example, U.S. Pat. Nos. 3,654,687 and 3,620,059.
As is clear from the above-mentioned patents, it is important that the billet is constructed so that pressure medium is prevented from penetrating between the core and the casing, since in that case no bond between the materials of the core and the casing can be obtained. The purpose of the invention is to improve the known method so that the production of billets can be simplified and made cheaper and the handling during the extrusion can be simplified and also the capacity in a given press be increased.
To be able to put together a core and a casing to form a billet, there is required a not insignificant play between the core and the casing, among other things because the casing is deformed upon the necessary annealing. It is bent and becomes oval. In a billet with an external diameter of the core of 150-160 mm there is required an internal diameter of the casing which is from 2 to 4 mm greater than the external diameter of the core. The play between the core and the casing thus becomes 1 to 2 mm. To obtain a manageable billet and a good seal there has been used in commercial production an end plug which has projected somewhat into the casing and a seal has been applied over the joint between the end plug and the casing. Between the end plug and the casing there has been a grip fit so that the plug has been fixed in the casing. This plug uses up space in the pressure chamber and must be removed and re-used. The other embodiments described require a small gap between the core and the casing, which is a disadvantage in commercial production.